1. Field of the Invention
The present invention relates to a silver layer formed by electrosilvering a substrate material.
2. Description of the Related Art
The silver layer has a high light reflectance (abbreviated to reflectance herein after), and thus it has widely been used for a reflecting plate of downlight illumination or a reflective surface of a light emitting diode (LED) package. In the case of the LED package, as a current input to the LED is increased until a predetermined light output is obtained, a life of the LED is greatly affected. Accordingly, in a high-output LED package applied for house illumination or main illumination of an automobile headlight or the like, spectral characteristics of the reflective surface are extremely important elements to decide product performance, requiring a reflectance as high as possible. Specifically, the silver layer has to have a high reflectance in all wavelength areas (400 to 700 nm) of visible lights. However, as a reflectance drops in a wavelength area of 400 to 500 nm near a LED excitation wavelength, it is important to increase the reflectance in this wavelength area. Under these circumstances, a method for increasing a reflectance of a silver layer, such as a method disclosed in Japanese Patent Application Laid-Open No. 2000-155205, has recently been proposed. According to this conventional method, however, as a silver layer is formed by electroless plating, it takes about 10 to 30 minutes to form a film with a thickness of 200 nm, and productivity is extremely low. Besides, running costs are high because a life of bathing used for the plating is short.
The present invention has been developed to solve the aforementioned problems, and it is an object of the invention to provide a silver layer high in productivity and reflectance in a visible light area, and its manufacturing method.
It is another object of the present invention to provide a LED mounted substrate which includes a silver layer high in productivity and reflectance in a visible light area as a reflective surface, and its manufacturing method.